1. Field of the Invention
The present invention relates to computer terminal systems and, more particularly, to user-programmable or pre-programmed terminals incorporating keyboard-display stations.
2. The Prior Art
Keyboard-display terminals of the prior art are exemplified by a cathode ray tube raster system of the type disclosed in U.S. Pat. No. 3,345,458, issued on Oct. 3, 1967, in the names of D. A. Cole et al, for Digital Storage And Generation Of Video Signals. The cathode ray tube conventionally includes a source for generating an electron beam, a screen on which different point locations are illuminated by impingement of the electron beam at different times, a horizontal control and a vertical control for positioning the electron beam with respect to the screen, and a video control for allowing and preventing the impingement of the electron beam on the screen in order to provide successive lines of dots. A character is produced on the screen in terms of a dot matrix and a row of characters is produced by a sequence of raster scans, each scan extending across the full width of the screen and illuminating a line of dots extending through all characters of the row. The dots on the screen correspond to bits of information derived from the central memory of the digital computer with which the keyboard-display terminal is associated. Conventionally, there has been one-to-one correspondence between display screen position and central memory location, an arrangement which has proved to be relatively inflexible with respect to character and attribute format and to be relatively inefficient with respect to central memory and buffer storage utilization.